1. Field of the Invention
The present invention relates to droplet deposition apparatus, particularly ink jet print heads, components therefore and methods for manufacturing such components.
2. Description of Related Art
A particularly useful form of inkjet printer comprises a body of piezoelectric material with ink channels formed, for example, by disc cutting. Electrodes can be plated on the channel facing surfaces of the piezoelectric material, enabling an electrical field to be applied to the piezoelectric xe2x80x9cwallxe2x80x9d defined between adjacent channels. With appropriate poling, this wall can be caused to move into or out of the selected ink channel, causing a pressure pulse which ejects an ink droplet through an appropriate channel nozzle. Such a construction is shown, for example, in EP-A-0 364 136.
It is a frequent requirement to provide a high density of such ink channels, with precise registration across a relatively large expanse of printhead, perhaps an entire page width. A construction that is useful to this end is disclosed in WO 98/52763. It involves the use of a flat base plate that supports the piezoelectric material as well as integrated circuits performing the necessary processing and control functions.
Such a construction has several advantages, particularly with regard to manufacture. The base plate acts as a xe2x80x9cbackbonexe2x80x9d for the printhead, supporting the piezoelectric material and integrated circuits during manufacture. This support function is particularly important during the process of buffing together multiple sheets of piezoelectric material to form a contiguous, pagewide array of ink channels. The relatively large size of the base plate also simplifies handling.
The plating produced for use in inkjet printing and in particular plating produced using electroless plating methods are not bonded to the printhead by chemical means and rely upon the surface topography to provide attachment points. The adhesives used typically in an inkjet printer do not provide a good surface for holding an electrode as the surface of the glues tend to be smooth. This leads to a poor bond between the adhesive and metal of the electrode and can result in lift off or breakage of the metal either during use or during further manufacturing stages. These problems cause reduced operation and can cause other defects such as electrical shorts. The present invention seeks to overcome this problem by using an adhesive that contains particles which provide keying points for improved bond strength.
Problems remain of reliably and efficiently establishing a uniform bond between the body of piezoelectric material and the substrate. In particular, a poorly formed glue layer gives rise to variations in the activity of the channel walls which in turn results in droplet deviations and consequently to a reduced quality of image. Crosstalk both electrical and mechanical between neighboring channels through the base of the piezoelectric material is also a problem that the present invention seeks to overcome.
Further problems result from the high level of flatness required from the substrate. A poorly finished substrate can give rise to a variation in the activity of channels across the width of the head, and can damage the saw when trying to cut channels of uniform depth since the material of the substrate can often be significantly harder that of the piezoelectric material.
The present invention seeks to provide improved apparatus and methods which address these problems.
According to one aspect of the present invention, there is provided a component suitable for use in a droplet deposition apparatus comprising a body of piezoelectric material having a top surface, and a bottom surface which is attached to a base, the body having a plurality of upper channels extending from the top surface into the piezoelectric body and a corresponding plurality of lower channels extending from the bottom surface of the body into the piezoelectric body; characterised in that the channels are of such a depth that there is a connection between at least one of the upper channel to a corresponding lower channel.
A second aspect of the present invention is found in a component suitable for use in a droplet deposition apparatus, the component being formed from a body of piezoelectric material and a base; the method comprising the steps of attaching the body to the base using an adhesive which contains particles having a stiffness greater than the stiffness of the adhesive, and sawing channels into the body.
A third aspect of the present invention consists in a method of forming a component for use in a droplet deposition apparatus comprising the steps of providing a base and a body of piezoelectric material having a top surface and a bottom surface, sawing lower channels into the bottom surface of the body, adhesively bonding said bottom surface of the body to the base by an adhesive layer, and subsequently sawing upper channels into the top surface of the body extending into the body; characterised in that the upper channels extend through the body and into the adhesive layer.
As known in the prior art the piezoelectric body can be made of a single block of piezoelectric material polarised in a single direction or a laminate of two blocks polarised in opposite directions. It has been noted by the applicant that problems can occur when applying actuating electrodes to the sawn channels of glued piezoelectric laminates in that a connection occasionally may not be formed across the bond. The present invention seeks to overcome this problem.
In a fourth aspect of the present invention a body of piezoelectric material formed from a laminate of two or more sheets having different polarisation directions is formed according to the following method: two or more sheets of piezoelectric material are provided and an adhesive is applied to one or more of said sheets of piezoelectric material which are subsequently joined to form the laminate; characterised in that the adhesive contains particles which have a stiffness greater than that of the adhesive.
In one embodiment of this aspect of the present invention, the piezoelectric sheets are polarised in opposite directions. In a further embodiment, the polarisation is perpendicular to the thickness of one or more of the sheet. In yet a further embodiment one or more of the sheets are polarised whilst the other sheets are unpoled, depoled or formed of a non piezoelectric material.
A fifth aspect of the present invention is a method of forming a component for use in a droplet deposition apparatus comprising the steps of providing a base (86), and a body (100) of piezoelectric material having a top surface and a bottom surface; sawing a plurality of lower channels (630) into the bottom surface of the body; bonding said bottom surface of the body to the base by adhesive means (710); and subsequently sawing a plurality of upper channels (7) into the top surface of the body; characterised in that at least one of the upper channels is sawn to such a depth that it extends through the body and connects to a corresponding lower channel.
Aspects of the present invention are also found in components formed using the above methods. A component suitable for use in a droplet deposition apparatus comprises a body of piezoelectric material having a top surface, and a bottom surface which is attached to a base, the body having a plurality of upper channels extending from the top surface into the piezoelectric body and a corresponding plurality of lower channels extending from the bottom surface of the body into the piezoelectric body; characterised in that the channels are of such a depth that at least one of the upper channels extends through the body to a corresponding lower channel so that a connection is formed between them.